Patients with well-documented post-transfusion chronic non-A, non-B (non-lupoid) hepatitis are being evaluated to determine the natural history of this disease and to obtain tissues and reagents to search for non-A, non-B agents. Thirty patients have been admitted to this study. These patients have undergone thorough evaluations including a liver biopsy. They have had the disease for periods ranging from 1 to 11 years. Seven patients have a mild degree of malaise, the remaining patients are asymptomatic. Liver biopsies have revealed chronic persistent hepatitis in seven, chronic active hepatitis in twenty-one and alcoholic liver disease in two. Six patients have developed cirrhosis. Trials of immunosuppressive and antiviral therapy for these patients are being planned. A pilot study of Acyclovir therapy has been carried out in five patients. No consistent effect of the drug on aminotransferase levels was observed. Serum aminotransferase activities are being determined routinely in all blood donors. Donors with elevated serum aminotransferase levels are followed and evaluated for the presence of non-A, non-B hepatitis and other liver diseases.